This is *not* an embarrassment you need to endure. You're in good company. From https://map.nrl.navy.mil/map/pub/nrl/NRLMSIS/NRLMSISE-00/NRLMSISE-00_jgra16630.pdf: "[ 57 ] The model accounts for the approximate spheroidal symmetry of the Earth and the atmosphere by incorporating a gravity field and an effective Earth radius which are both latitude-dependent and by using spherical harmonics to represent spatial variability of the key parameters that define temperature and species number density profiles." I didn't know about this model until a few weeks ago, and it fills in a lot of difficulties seen when using Standard Atmosphere models applied to LEO. These are some less-heavy documents about the model: https://en.wikipedia.org/wiki/NRLMSISE-00 https://ccmc.gsfc.nasa.gov/models/NRLMSIS~00/ A_J On 31-Jan-26 16:54, Robert McNaught via Seesat-l wrote: > Thanks for your summary Marco. The breakup up or payload hypotheses > make sense for the double TIP. > > For a few years I've been hoping to get a near reentry situation of an > eccentric orbit with low perigee near my latitude. This would > potentially give multiple opportunities to observe the object ablating > but not fully reenter. In the case of ZQ-3 RB, the perigee has been > drifting north due to precession from the southern apex of 57S on Jan > 10 and was at 43S on Jan 29. The last orbit shows a jump to 38S as the > drift becomes more stocastic due to drag at perigee rather than the > the gravitational effect of the Earth's oblateness. > > I have an embarrassing question which I never really investigated > properly. The standard equation for perigee and apogee subtracts the > Earth's equatorial radius to give height. For the final orbit this was > 102 x 211 km. However, the height above the spheroid for perigee at > 38S would be 111 x 219 km. I always assumed the atmospheric density is > not dependent on latitude for a given height above the spheroid, but > is that true? If true, a truly circular orbit would experience maximum > drag on crossing the equator. > > In the NEA realm, tangential "reentries" have been observed on a > number of occasions, although in these cases with hyperbolic > geocentric orbits. There are thus thus asteroids in solar orbit with > ablated surfaces. A stable orientation during "reentry" would produce > an asteroid with one ablated hemisphere and the other unablated. > > Cheers, Rob > > On 31/01/2026 18:25, Marco Langbroek via Seesat-l wrote: >> >> Blog post on this: >> >> https://sattrackcam.blogspot.com/2026/01/you-only-die-twice-redux-unusual-and.html >> >> >> - Marco >> >> Op 31-1-2026 om 17:58 schreef Marco Langbroek via Seesat-l: >>> >>> Hi Rob a.o., >>> >>> I just saw this, and never seen it before. Very odd! >>> >>> One explanation could be the following: >>> >>> The ZQ-3 RB reentry was from a somewhat eccentric orbit (more so >>> than your average reentry. The last available orbit was 211 x 102 km. >>> >>> The 12:39 UTC first "reentry" point could be where the R/B started >>> to ablate and fragment near perigee. One relatively massive fragment >>> however might have survived perigee and finally reentered half an >>> orbital revolution later at 13:43 UTC. >>> >>> I wonder whether that fragment was the dummy payload, still attached >>> to the upper stage, that might have come loose during the first >>> "reentry" moment and survived, for example because it was a massive >>> dummy mass with relatively large weight to size, while the rest of >>> the R/B (the R/B proper) reentered at the 12:30 first reentry point. >>> >>> Just an hypothesis, I am open to other explanations (including one >>> of the two being an "artifact"/"ghost detection"). >>> >>> - Marco >> >> _______________________________________________ >> Seesat-l mailing list >> https://lists.seesatmail.org/mailman/listinfo/seesat-l > > > _______________________________________________ > Seesat-l mailing list > https://lists.seesatmail.org/mailman/listinfo/seesat-l _______________________________________________ Seesat-l mailing list https://lists.seesatmail.org/mailman/listinfo/seesat-lReceived on Mon Feb 02 2026 - 12:17:56 UTC
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